This invention relates to packaging of products such as fresh red meat products and the like, and particularly relates to a vacuum skin package having a peelable barrier layer and a method for making same.
Skin packaging can be classified as a vacuum forming process for thermoformable polymeric films. The product on a supporting member serves as the mold for the thermoformable film which is formed about the product by means of differential air pressure. However, the term "vacuum skin packaging" or VSP as it is referred to hereinafter, refers not only to the fact that the thermoformable film is formed around the product by vacuum or differential air pressure but also to the fact that the product is packaged under vacuum and the space containing the product is evacuated. Thus, there is a need for the film formed around the product and for the support member to be a barrier to oxygen, air, and other gases.
In conventional skin packaging, a backing board which is porous or which is perforated so that a vacuum may be drawn directly through the backing board is employed. In vacuum skin packaging processes generally a vacuum chamber with an open top is used. The product on an impervious backing board is placed on a platform within the vacuum chamber. The top of the chamber is covered by a sheet of film which is clamped tightly against the chamber to form a vacuum tight closure. The chamber is evacuated while the film is heated to its forming and softening temperature. The platform is then raised to drive the product into the softened film and air pressure can be used above the film to force it tightly around the product. A process of this type is disclosed in French Patent No. 1,258,357 which issued to Alain G. Bresson on Mar. 6, 1961.
A variant of the process described in the Bresson patent is disclosed in French Patent No. 1,286,018 which issued on Jan. 22, 1962 to LaRoach Freres Limited. In the LaRoach Freres process, after the chamber has been evacuated and the product driven into the heat softened film, the vacuum is released and ambient air is permitted to enter the chamber so that the thermoplastic film molds more or less onto the product since there is a vacuum on the product side of the film and ambient air pressure on the other side of the film. Australian Patent No. 245,774 which issued to Colbros Proprietary Limited et al on Jul. 16, 1967 discloses a vacuum skin packaging process in which an article to be packaged is inserted within the lower half of a vacuum chamber on a backing board, a thermoplastic film is placed over the open face of the lower half of the chamber, the chamber is closed and both halves are brought to essentially the same state of vacuum, the film is heated and softened, and then atmospheric air is introduced into the upper half of the chamber so that it alone forces the thermoplastic film down around the product and against the backing board.
Another prior art version of vacuum skin packaging is disclosed in U.S. Pat. No. 3,491,504, which issued to W. E. Young et al on Jan. 27, 1970, heat softened film is physically moved down over a stationary product and, in connection with air pressure, the softened thermoplastic film is molded onto the product.
In U.S. Pat. No. Re. 30,009, which was reissued on May 29, 1979 to Richard R. Perdue et al, a thermoformable or heat softenable film sheet is drawn by differential air pressure against the concave interior surface of the upper portion of a vacuum chamber, the film is then heated by surface contact, and then, after evacuation of the chamber, air pressure is used to blow the heat softened film down over the product and against the backing board. The resulting package comprises the product positioned on the backing board which is gas impervious and the product is held there by the thermoformable film which has been formed around the product in the exact shape of the product so that it appears to be a "skin." The thermoformable film, as stated previously, is also gas impervious and usually will consist of a number of layers each of which performs a specific function. The product contact and backing member contact layer will be a sealing or heat sealable layer, an interior layer will typically be a barrier layer which comprises a vinylidene chloride copolymer (PVDC) or a hydrolyzed ethylene/vinyl-acetate copolymer (EVOH), and the outer surface layer will be an abuse layer to protect the barrier layer from scratches, pin holes, moisture attack and the like.
In U.S. Pat. No. 3,574,642 which issued on Apr. 13, 1971 to Carl Frederick Weinke, a package for and a method of packaging meats is disclosed. The package includes an inner oxygen-permeable member which may be either gas flushed or evacuated. The package preserves the freshness of the meat until the meat is ready to be marketed to the consumer. For marketing, the outer wrapper is removed and the inner package is displayed at the meat counter for the consumer. Being oxygen-permeable, the inner wrapper admits oxygen to the interior of the package causing the fresh meat product to change to a bright red color which the consumer associates with freshness. The inner pouch of the Weinke package may consist of polyethylene film and the outer pouches may be cellophane film with a coating of saran (vinylidene chloride copolymer or PVDC.) Another patent showing portions of fresh meat individually packaged in oxygen permeable plastic film and inserted into an outer container of impermeable film is U.S. Pat. No. 3,681,092 which issued to Oliver R. Titchness et al on Aug. 1, 1972.
Another prior art package is described in U.S. Pat. No. 3,713,849 which issued to Paul E. Grindrod et al on Jan. 30, 1973. In the Grindrod et al patent a fresh meat package having an outer oxygen impermeable lamina which is readily and entirely peelable from an inner oxygen-permeable lamina is disclosed. The package includes means for initiating the peeling separation along an edge of the package. The outer oxygen barrier maintains meats in well preserved condition in spite of the purplish color which has low consumer appeal. Shortly prior to display for sale to the consumer the outer lamina is removed by the retailer and the product develops a healthy, bright red "bloom" due to the high rate of oxygen permeation through the inner remaining film package. The material disclosed in Grindrod et al is a laminate of PVC/Saran and EVA/Saran. (EVA designates ethylene/vinyl-acetate copolymer and PVC designates polyvinyl-chloride.) The EVA and PVC layers are the inner layers and at the periphery of the package they are sealed together but form a weak bond. The saran layers can be readily peeled from the respective EVA or PVC layers as saran does not form a strong bond between either. Gripping tabs are also provided.
Yet another peelable package is shown in U.S. Pat. No. 4,055,672 which issued on Oct. 25, 1977 to Arthur Hirsch et al. In the Hirsch et al patent a semi-rigid tray of oxygen impermeable material is formed, a meat product placed therein, and then the tray is sealed around its upper periphery or flange area by a composite lid which has an inner layer of oxygen permeable material, an adhesive layer, and an outer layer of oxygen impermeable material. When the package is ready for retail display so that oxygen can reach the fresh meat packaged within the tray, the outer impermeable lid is peeled away so that the oxygen can penetrate through the remaining oxygen permeable portion of the lid.
In order to readily open packages where plastic film layers have been sealed together to close the package, various tear tabs and easy open mechanisms have been devised. One such easy-to-open, delaminating seal is disclosed in U.S. Pat. No. 4,638,913 which issued on Jan. 27, 1987 to Milton A. Howe, Jr. In this patent, two grippable film folds are provided and the folds when pulled apart will rupture one of the outer layers of the sealed together film and delaminate the film to its edge.
The aforedescribed tear tabs and easy open mechanisms typically involve the rupturing of the non-barrier or oxygen permeable layer so that the portion of the non-barrier layer which is included in a pull tab is separated for removal while the remaining non-barrier layer remains sealed in place over the product as desired. To provide this feature, "non-stick" tabs are disposed between the non-barrier layer and the bottom web, and perforations, score lines and the like may be necessary to reduce the internal strength of the non-barrier layer so that it will rupture when and where it is desired.
It would be desirable to provide a package wherein peeling does not require rupturing of one of the layers.
It is therefore the principal object of the invention to provide a package and a method for packaging wherein a barrier layer is readily peelable without rupturing the non-barrier layer.
It is a further object of the invention to provide a package and packaging method wherein extra material for pull tabs is not needed.
It is a still further object of the invention to provide a method for making a package wherein conventional packaging equipment can be used.
Other objects and advantages will appear hereinbelow.